The recapping of tires with flexible molds has heretofor been accomplished by first building up a layer of uncured rubber on a buffed tire carcass. A flexible ring mold having a negative tread pattern imprint is then placed around the built-up tire and the whole assembly placed in a sealing envelope. This whole assembly is then placed into a vulcanizing chamber and the rubber is cured with the imprint of the mold contained therein.
During placement of the mold over the built-up tire, the mold must be stretched and expanded to allow the tread pattern to fit around the built up tire. Alternatively, the tire must be "buckled" to receive the mold and then inflated against the mold. During curing of the rubber with the mold so disposed, the rubber assumes a plastic state, thereby allowing the mold tread pattern to sink into the rubber to form the positive contour of the tread. This process is normally assisted by some form of external force such as high chamber pressure applied to the mold, the aspiration and resiliency of the sealing envelope or pressure applied to the built up tire to force outward against the mold.
A prior retread method utilizing a flexible continuous mold is disclosed in U.S. Pat. No. 4,053,265 issued to Wulker on Oct. 11, 1977. The Wulker patent discloses an expandable continuous or ring mold that is resilient enough to resume its initial state after it is stretched and disposed about the tire. However, several disadvantages exist in this type of mold in that the mold is difficult to stretch for disposal about the tire. This process is relatively difficult and usually requires expensive equipment and often more than one operator to place the mold about the tire. If the mold is not properly placed about the tire, misalignment of tread design can occur which would result in a reject. Moreover, repeated stretching of such prior molds can cause deterioration of the molds.
Ring molds of this type also have the disadvantage that a separate ring mold must be provided for each tire size and each ring mold must accommodate all variances in a given tire size. Depending upon the tire size, the circumference between various tires within a particular size can vary as much as one to five inches. As the tire size varies, the clearance between the mold and the built up tire also varies. This variance results in additional problems in placing the mold on the built-up tire and can cause misalignment of the tread pattern during the handling and vulcanization process.
In view of the above, there exists a need for a tire retreading process that utilizes a mold that is relatively easy for an operator to utilize and which accommodates the variations in a given tire size.